When compiling the example sketch for adafruit OLED display, the sketch refers to Adafruit_GFX and consequently to fontconvert.c
This file includes a header file named ft2build.h, which many of the compilers fail to find, resulting in compilation error.
Check the discussion on this issue: https://github.com/adafruit/Adafruit-GFX-Library/issues/88
Simply adding two lines solves the problem.
